Heat shock and cold shock in Deinococcus radiodurans

On the basis of acquired thermotolerance and cryotolerance, the optimal heat shock and cold shock temperatures have been determined for Deinococcus radiodurans. A heat shock at 42°C maximized survival at the lethal temperature of 52°C and a cold shock at 20°C maximized survival after repeated freeze-thawing. Enhanced survival from heat shock was found to be strongly dependent on growth stage, with its greatest effect shortly after phase. Increased synthesis of a total of 67 proteins during heat shock and 42 proteins during cold shock were observed by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) and autoradiography. Eight of the most highly induced heat shock proteins shown by 2D PAGE were identified by MALDI-MS as Hsp20, GroEL, DnaK, SodA, Csp, Protease I and two proteins of unknown function.     

Caveolin internalization by heat shock or hyperosmotic shock

We investigated the cellular localization of caveolin, a landmark protein of caveolae, by indirect immunofluorescence after heat shock or hyperosmotic shock. Caveolin was internalized to the perinucleus by heat shock (43 degrees C) and relocalized in the plasma membrane after recovery of NIH3T3 cells at 37 degrees C for 4 h. The caveolin internalization was also observed after cells were exposed to hyperosmotic shock. Caveolin disappeared from detergent-insoluble complexes in the heat-shocked cells, but alkaline phosphatase was still there, suggesting that their responses to heat shock are quite different even though both of them were enriched in detergent-insoluble complexes of normal cells. Caveolin was internalized by the actin depolymerizer cytochalasin D, but not by the tubulin depolymerizer nocodazole. In addition, cellular exposure to hydrogen peroxide caused caveolin internalization along with disintegrated microfilaments and intact microtubules. Since cellular exposure to heat shock showed disintegrated microfilaments but intact microtubules, caveolin internalization might be due to depolymerized microfilaments. When cells were exposed to heat shock and allowed to recover for 4 h, actin depolymerization and caveolin internalization were not induced by a second heat shock, suggesting that some heat shock protein(s) might prevent actin depolymerization and caveolin internalization.     

Cargiogenic shock

A healthy male newborn was submitted to his first-day three-dimensional (3D) echocardiogram (see movie clip on the journal’s website at http://www.cardiologie.nl). Physical examination was normal.     

Heat shock proteins and effects of heat shock in plants

Soybean seedlings when exposed to a heat shock respond in a manner very similar to that exhibited by cultured cells, and reported earlier [2]. Maximum synthesis of heat shock proteins (HSPs) occurs at 40C. The heat shock response is maintained for a relatively short time under continuous high temperature. After 2.5 hr at 40 C the synthesis of HSPs decreases reaching a very low level by 6 hr. The HSPs synthesized by cultured cells and seedlings are identical and there is a large degree of similarity in HSPs synthesized between the taxonomically widely separated species, soybean and corn. Storage protein synthesis in the developing soybean embryo is not inhibited but is actually stimulated during a heat shock, unlike most other non-HSPs, whose synthesis is greatly reduced. Seedlings respond differently to a gradual increase in temperature than they do a sudden heat shock. There is an upward shift of several degrees in the temperature at which maximum protein synthesis occurs and before it begins to be inhibited. In addition, there appears to be a protection of normal protein synthesis from heat shock inhibition when the temperature increase is gradual. An additional function of the heat shock phenomenon might be the protection of seedlings from death caused by extreme heat stress. The heat shock response appears to have relevance to plants in the field.